When painting the portrait of the Queen, at what point does an artist decide his work is good enough?

Only a handful of artists in the world know the answer to that question, among them Wellington artist Nick Cuthell, who said he was in a state of ‘‘despair’’ at the end. ‘‘I’m always in despair when I finish a painting, I think ‘oh God, it’s never good enough’.

‘‘But I suppose that’s what keeps you going, but I feel I did my best and that’s all you can do,’’ he said.

Cuthell was commissioned to do the painting, which was paid for by an anonymous donor group.

It was unveiled by Prince William last night, at a state reception for both him and his wife Catherine, the Duchess of Cambridge, who are part way through a 10-day tour of New Zealand. The painting of the Queen took some months to complete, but Cuthell had just one hour to get what he needed from his subject.

‘‘I had one sitting with her of an hour, which is not long, but I gather it’s about as long as you can get these days,’’ he said. Most artists only get to work with photographs.

‘‘It’s certainly better than having no time at all. It just makes such a difference to see a human being in space and light, with your eyes as opposed to a photograph.’’

It was Cuthell who requested the Queen wear a blue day dress, with the New Zealand Silver Fern brooch that was gifted to her in 1953. The same brooch is now on loan to the Duchess of Cambridge as she tours through the country.

He said the first five minutes were spent getting photographs of her in position but the Queen, who is now 87, had spent the morning standing through an investiture ceremony.

‘‘I didn’t want to make her stand too long. So then she sat in the chair and I just made a kind of head study – an oil sketch for about 15 minutes and yeah, we chatted the whole time.

‘‘One of the other things that’s important to do in that session I think, is to just get a sense of the human being and develop something of a relationship or a feeling for that person, so that was what that was about.’’

‘‘Honestly, it’s a dream come true for me. If you’d asked me five or ten years ago ‘if you could do anything, or paint anyone, who would it be?’ I would have said the Queen, thinking ’that’ll never happen,’’’ he said.

‘‘She must have one of the toughest jobs in the world and she does it with grace and elegance and dignity as far as I can see.’’

An image had been sent to the palace, but Cuthell said the Queen had not commented on it – he wasn’t sure if she’d even seen it. But he wasn’t fazed.

‘‘I think the palace doesn’t comment on portraits, which I think is absolutely the right thing to do. ‘‘

But within minutes of the portrait being unveiled in front of local and foreign press, images of it were sent across the world.

‘‘Am I nervous, yeah definitely. Lots of people are going to see it, I mean by virtue of the Duke and Duchess, who are just the most glamorous couple in the world right now, so everyone’s watching them, and then wondering ‘‘whose that in the background’’, oh it’s her majesty the Queen.

‘‘I painted that, so yeah, people will be looking. But that’s okay, you don’t paint a painting hoping people won’t look at it.’’

And you’d be mistaken if you thought Cuthell had reached the pinnacle of portrait painting.

He said he would be ‘‘having a word to the Duchess of Cambridge’’ asking of her plans for the immediate future.

‘‘And her husband of course, the whole family.’’

Cuthell has had an interesting career, with portrait highlights including that of Sir Ian McKellen, with whom he famously turned heads at the 2002 Academy Awards, when he appeared as McKellen’s then boyfriend.

Cuthell also painted the portraits of many of the cast of The Hobbit, and recently was commissioned to paint Alan Bollard when he retired as Reserve Bank governor. He has also had commissions in London and Florence, Italy, where he studied.